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Commit226ec49

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Fix division-by-zero error in to_char() with 'EEEE' format.
This fixes a long-standing bug when using to_char() to format anumeric value in scientific notation -- if the value's exponent isless than -NUMERIC_MAX_DISPLAY_SCALE-1 (-1001), it produced adivision-by-zero error.The reason for this error was that get_str_from_var_sci() divides itsinput by 10^exp, which it produced using power_var_int(). However, theunderflow test in power_var_int() causes it to return zero if theresult scale is too small. That's not a problem for power_var_int()'sonly other caller, power_var(), since that limits the rscale to 1000,but in get_str_from_var_sci() the exponent can be much smaller,requiring a much larger rscale. Fix by introducing a new function tocompute 10^exp directly, with no rscale limit. This also allows 10^expto be computed more efficiently, without any numeric multiplication,division or rounding.Discussion:https://postgr.es/m/CAEZATCWhojfH4whaqgUKBe8D5jNHB8ytzemL-PnRx+KCTyMXmg@mail.gmail.com
1 parent87bff68 commit226ec49

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3 files changed

+76
-29
lines changed

3 files changed

+76
-29
lines changed

‎src/backend/utils/adt/numeric.c

Lines changed: 37 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -428,16 +428,6 @@ static const NumericDigit const_two_data[1] = {2};
428428
staticconstNumericVarconst_two=
429429
{1,0,NUMERIC_POS,0,NULL, (NumericDigit*)const_two_data};
430430

431-
#ifDEC_DIGITS==4||DEC_DIGITS==2
432-
staticconstNumericDigitconst_ten_data[1]= {10};
433-
staticconstNumericVarconst_ten=
434-
{1,0,NUMERIC_POS,0,NULL, (NumericDigit*)const_ten_data};
435-
#elifDEC_DIGITS==1
436-
staticconstNumericDigitconst_ten_data[1]= {1};
437-
staticconstNumericVarconst_ten=
438-
{1,1,NUMERIC_POS,0,NULL, (NumericDigit*)const_ten_data};
439-
#endif
440-
441431
#ifDEC_DIGITS==4
442432
staticconstNumericDigitconst_zero_point_nine_data[1]= {9000};
443433
#elifDEC_DIGITS==2
@@ -582,6 +572,7 @@ static void power_var(const NumericVar *base, const NumericVar *exp,
582572
NumericVar*result);
583573
staticvoidpower_var_int(constNumericVar*base,intexp,NumericVar*result,
584574
intrscale);
575+
staticvoidpower_ten_int(intexp,NumericVar*result);
585576

586577
staticintcmp_abs(constNumericVar*var1,constNumericVar*var2);
587578
staticintcmp_abs_common(constNumericDigit*var1digits,intvar1ndigits,
@@ -7210,9 +7201,7 @@ static char *
72107201
get_str_from_var_sci(constNumericVar*var,intrscale)
72117202
{
72127203
int32exponent;
7213-
NumericVardenominator;
7214-
NumericVarsignificand;
7215-
intdenom_scale;
7204+
NumericVartmp_var;
72167205
size_tlen;
72177206
char*str;
72187207
char*sig_out;
@@ -7249,25 +7238,16 @@ get_str_from_var_sci(const NumericVar *var, int rscale)
72497238
}
72507239

72517240
/*
7252-
* The denominator is set to 10 raised to the power of the exponent.
7253-
*
7254-
* We then divide var by the denominator to get the significand, rounding
7255-
* to rscale decimal digits in the process.
7241+
* Divide var by 10^exponent to get the significand, rounding to rscale
7242+
* decimal digits in the process.
72567243
*/
7257-
if (exponent<0)
7258-
denom_scale=-exponent;
7259-
else
7260-
denom_scale=0;
7261-
7262-
init_var(&denominator);
7263-
init_var(&significand);
7244+
init_var(&tmp_var);
72647245

7265-
power_var_int(&const_ten,exponent,&denominator,denom_scale);
7266-
div_var(var,&denominator,&significand,rscale, true);
7267-
sig_out=get_str_from_var(&significand);
7246+
power_ten_int(exponent,&tmp_var);
7247+
div_var(var,&tmp_var,&tmp_var,rscale, true);
7248+
sig_out=get_str_from_var(&tmp_var);
72687249

7269-
free_var(&denominator);
7270-
free_var(&significand);
7250+
free_var(&tmp_var);
72717251

72727252
/*
72737253
* Allocate space for the result.
@@ -10519,6 +10499,34 @@ power_var_int(const NumericVar *base, int exp, NumericVar *result, int rscale)
1051910499
round_var(result,rscale);
1052010500
}
1052110501

10502+
/*
10503+
* power_ten_int() -
10504+
*
10505+
*Raise ten to the power of exp, where exp is an integer. Note that unlike
10506+
*power_var_int(), this does no overflow/underflow checking or rounding.
10507+
*/
10508+
staticvoid
10509+
power_ten_int(intexp,NumericVar*result)
10510+
{
10511+
/* Construct the result directly, starting from 10^0 = 1 */
10512+
set_var_from_var(&const_one,result);
10513+
10514+
/* Scale needed to represent the result exactly */
10515+
result->dscale=exp<0 ?-exp :0;
10516+
10517+
/* Base-NBASE weight of result and remaining exponent */
10518+
if (exp >=0)
10519+
result->weight=exp /DEC_DIGITS;
10520+
else
10521+
result->weight= (exp+1) /DEC_DIGITS-1;
10522+
10523+
exp-=result->weight*DEC_DIGITS;
10524+
10525+
/* Final adjustment of the result's single NBASE digit */
10526+
while (exp-->0)
10527+
result->digits[0] *=10;
10528+
}
10529+
1052210530

1052310531
/* ----------------------------------------------------------------------
1052410532
*

‎src/test/regress/expected/numeric.out

Lines changed: 32 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1794,6 +1794,38 @@ FROM v;
17941794
NaN | #.####### | #.####### | #.#######
17951795
(7 rows)
17961796

1797+
WITH v(exp) AS
1798+
(VALUES(-16379),(-16378),(-1234),(-789),(-45),(-5),(-4),(-3),(-2),(-1),(0),
1799+
(1),(2),(3),(4),(5),(38),(275),(2345),(45678),(131070),(131071))
1800+
SELECT exp,
1801+
to_char(('1.2345e'||exp)::numeric, '9.999EEEE') as numeric
1802+
FROM v;
1803+
exp | numeric
1804+
--------+----------------
1805+
-16379 | 1.235e-16379
1806+
-16378 | 1.235e-16378
1807+
-1234 | 1.235e-1234
1808+
-789 | 1.235e-789
1809+
-45 | 1.235e-45
1810+
-5 | 1.235e-05
1811+
-4 | 1.235e-04
1812+
-3 | 1.235e-03
1813+
-2 | 1.235e-02
1814+
-1 | 1.235e-01
1815+
0 | 1.235e+00
1816+
1 | 1.235e+01
1817+
2 | 1.235e+02
1818+
3 | 1.235e+03
1819+
4 | 1.235e+04
1820+
5 | 1.235e+05
1821+
38 | 1.235e+38
1822+
275 | 1.235e+275
1823+
2345 | 1.235e+2345
1824+
45678 | 1.235e+45678
1825+
131070 | 1.235e+131070
1826+
131071 | 1.235e+131071
1827+
(22 rows)
1828+
17971829
WITH v(val) AS
17981830
(VALUES('0'::numeric),('-4.2'),('4.2e9'),('1.2e-5'),('inf'),('-inf'),('nan'))
17991831
SELECT val,

‎src/test/regress/sql/numeric.sql

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -939,6 +939,13 @@ SELECT val,
939939
to_char(val::float4,'9.999EEEE')as float4
940940
FROM v;
941941

942+
WITH v(exp)AS
943+
(VALUES(-16379),(-16378),(-1234),(-789),(-45),(-5),(-4),(-3),(-2),(-1),(0),
944+
(1),(2),(3),(4),(5),(38),(275),(2345),(45678),(131070),(131071))
945+
SELECT exp,
946+
to_char(('1.2345e'||exp)::numeric,'9.999EEEE')asnumeric
947+
FROM v;
948+
942949
WITH v(val)AS
943950
(VALUES('0'::numeric),('-4.2'),('4.2e9'),('1.2e-5'),('inf'),('-inf'),('nan'))
944951
SELECT val,

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